They'll find someone else who can do a similar voice. Even putting aside the anime, they'd still need someone to voice games for example.
Lupin III was recast in 1995 after having the same voice since 1971 (aside from a movie that was seen very negatively exactly because it didn't use the original VAs). The Japanese give a lot of importance to VA, but they won't kill a franchise alongside them.
Yeah. I'm pretty sure Luffy/Krillin's voice actor is up there with Nozawa, but they wouldn't just cancel the One Piece anime if she wasn't able to do VA work anymore.